AE Preset: Back N Forth

Back N Forth is a free sine wave generator preset for the position, scale, and rotation in every axis of your objects inside of After Effects...

What this means is that with this preset, you can automatically make your layers move from side to side (or up and down) in a motion that is always equidistant from the center on both ends! This is different from using something like “Wiggle” in that wiggle is more or less random motion, whereas sin waves are constant and fluid.

Not disimilar is Ease and Wizz, a script to generate alternative keyframe interpolations for After Effects (especially to the sine-like Easy Ease). Looking at pictures by Chris Meyer is the fastest way to see what behaviors you get with this script. Author Ian Haigh has a nice demo on AE Scripts; here's a preview:

Continuing with tangents off sine animation are some tutorials for creating animation of sines: